Degradation picks are known to be used in such fields as road milling, mining and trenching to engage and degrade tough materials such as asphalt, concrete and rock. Such degradation picks may be secured to an exterior of a rotatable drum so as to be repeatedly brought into contact with a surface of a material to be degraded. Each degradation pick may comprise a hardened tip designed for repeated impact with a tough material. Such repeated impact may break up the tough material into aggregate pieces. To secure such degradation picks to a rotatable drum, a generally cylindrical shank opposite the hardened tip may be disposed within a bore within a block that is rigidly fixed to the drum.
It may be desirable to position additional degradation picks in strategic locations around a rotatable drum. For example, the ends of a rotatable drum when viewed along a rotational axis thereof may engage tough materials not only around a perimeter of the drum but also beyond the end of the drum. In such cases, it may be desirable to position additional degradation picks proximate the end of the drum to engage this additional material.
Additional degradation picks may be disposed proximate an end of a drum by attaching a ring to an end of a drum to hold additional degradation pick blocks. For example, U.S. Pat. No. 4,225,190 to Hoffmann describes a mining auger which is used in the underground mining of coal comprising an end ring along its outer periphery. A plurality of tool holders is provided along a free edge of the end ring. The longitudinal axis of each tool holder coincides with the longitudinal axis of each cutting tool bit arranged in the respective tool holder.
By way of another example, U.S. Pat. No. 4,411,475 to Best et al. describes a cutting drum for an extracting machine assembled of a base body having a frustoconical configuration and an end ring which is detachably mounted to a major end face of the base body. The end ring is provided along its periphery with a plurality of tool holders for accommodating picks.
Despite these advancements in the art, the need for even tighter formations of degradation picks than those possible by arranging tool holders around the periphery of an end ring is still desirable. This is because each of the tool holders occupies a given footprint thus limiting the number that may fit in any defined area.